is my interpreation correct

[Sharan Basappa]

A code I am using as reference has the following line:
from nltk.stem.lancaster import LancasterStemmer

I am inferring the following based on above:
1) nltk is a package
2) nltk itself may have module because I see - nltk.word_tokenize(pattern['sentence']) in the code
3) nltk has a package named stem which has another package named Lancaster that has LancasterStemmer package

Somehow, I get confused with what is the package, module and function in third party packages like above.